Investigations on rate constants of the charging/discharging processes for metal hydride electrodes

Based on the energy barrier theory, we proposed a kinetics investigation method to research the rate constants of the charging/discharging processes for the metal hydride electrodes. The Tafel polarization curves and galvanostatic intermittent titration technique (GITT) method were applied to characterize the electrochemical parameters of the electrode reactions. In this paper, the values of the standard Gibbs free energy and the rate constants obtained from different over-potentials and various depth of discharge (DOD) were compared. Both the rate constants of the charging/discharging reactions decreased with the increase of DOD, which were in agreement with the variations of the hydrogen diffusion coefficient. The proposed method is more visualized and accurate for studying the reaction rates of the metal hydride electrodes and can be used to quantitatively investigate the kinetics properties of the Ni/MH batteries.

► The equations for the rate constants were obtained based on the energy barrier theory.
► The variations of the rate constants were in agreement with the diffusion coefficient.
► The method can quantitatively study the reaction rates of the Ni/MH batteries.